Electrodynamic apparatus for controlling flow of particulate material

ABSTRACT

Flow of particulate material along a defined path is controlled electrodynamically by means of elongated electrodes curved concentrically to the path, as axially spaced rings or interwound spirals. Each electrode is axially spaced from its neighbors by a distance about equal to its diameter and is connected with one terminal of a multi-phase alternating high voltage source. Adjacent electrodes along the path are connected with different terminals in a regular sequence, producing a wave-like nonuniform electric field that repels electrically charged particles axially inwardly and tends to propel them along the path.

United States Patent 11 1 Masuda 1*Mar. 18, 1975 ELECTRODYNAMICAPPARATUS FOR CONTROLLING FLOW OF PARTICULATE [56] References CitedMATERIAL UNITED STATES PATENTS Inventor: Senichi s a, 0- 5, 3,778,678 121973 Masuda 317 3 l-chome, Nishigahara, Kita-ku, Tokyo' Japan PrimaryE.\'ami11er-J. D. Miller Notice; The portion f the term f this AssistantE.\71minerHarry E. Moose. Jr.

patent subsequent to Dec. ll, 1990, has been disclaimed. [57] ABSTRACT[22] Filed: Oct. 18, 1973 Flow of particulate material along a definedpath is controlled eleetrodynamically by means of elongated [211 App!407436 electrodes curved concentrically to the path, as axially RelatedU.S. Application Data spaced rings or interwound spirals. Each electrodeis [63] Continuation-in-part of Ser. No. 366,655, June 4, axially Spacedfrom its neighbors y a distance about 1973, which is a continuation of Sr, Nu 151,789 equal to its diameter and 1s connected with one termi-June 10. 1971 which is a continuation of Ser. No. nal of a multi-phasealternating high voltage source. 2373422 March 24. 1972 Pat. No.3.806,763. Adjacent electrodes along the path are connected withdifferent terminals in a regular sequence, producing a [52] -S- C 6 l /3wave-like nonuniform electric field that repels electri- [511 int. Cl.HObS 5/02 ll harged particles axially inwardly and tends to [58 Field OfSearch 317/3, 262 R, 262 E; propel them along the path.

4 Claims, 3 Drawing Figures ELECTRODYNAMIC APPARATUS FOR CONTROLLINGFLOW OF PARTICULATE MATERIAL This application is a continuation-in-partof each of the applicants copending applications Ser. No. 366,655, filedJune 4, 1973 as a continuation of Ser. No. 151,789, filed June 10, 1971;and Ser. No. 237,822, filed Mar. 24, 1972 now Pat. N o, 3, 80 6 ,7 63;

and inasmuch as the present application contains only subject matterdisclosed in those applications, this application constitutes aconsolidation of portions of those applications. There is being filed inconnection with this application a terminal disclaimer which effectsexpiration of the patent issuing hereon concurrently with expiration ofthe patent issuing on applicants copending allowed application, Ser. No.226,750, filed Feb, 16, 1972 now Pat. No. 3,778,678.

This invention relates to apparatus for controlling the movement ofparticulate material along a defined path while confining the materialto a zone near the centerline of that path; and the invention is moreparticularly concerned with apparatus whereby such control of themovement of powder-like material is effected substantially withoutpermitting contact between the material and a solid surface and whilethe material is maintained in a loose and uncompacted state, that is,with its particles not adhering or cohering to one another.

The general object of the present invention is to provide apparatus bywhich powder-like particulate material can either be transported along adefined elongated path or stopped or otherwise controlled in itsmovement along such a path, at the same time that such material isconfined to a zone near the centerline of the path and against lateraldispersion into contact with surface areas of solid material which aresubstantially concentric with that centerline.

Thus one of the specific objects of the invention, achieved in certainembodiments of it, is to provide means for causing coloring powder orother particulate material to move along a substantially horizontallydisposed tube at a controlled rate, from a source of the material nearone end of the tube to a destination zone or point of application nearthe other end of the tube, with the material uncompacted and loose inthe tube and more or less levitated to be substantially out of contactwith the tube surfaces.

Another specific object of the invention, realized in other embodimentsthereof, is to provide apparatus by which a stream of particulatematerial, dropping from a source thereof under the influence of gravity,can be causedto flow intermittently, with flow being con trolledlystarted and stopped as desired, so that a valvelike operation can beobtained although the apparatus includes no valve element or itsequivalent, and with the material being at all times more or lesslevitated in a loose, cloud-like condition so that free and steady flowof the material is obtained at times when discharge is desired.

It will be apparent that the apparatus of the present invention isuseful, in general, for transporting a variety of kinds of particulatematerial and metering or feeding such material out of a source or supplythereof, and that the apparatus is thus generally useful for such variedpurposes as powder spray painting and coating, printing and decoratingvarious articles, classifying particles as to size, and otherwiseguiding and controlling the flow of powder and particulate materials.

In general the objects of the invention are achieved with apparatuscomprising elongated concentrically curved electrodes that are soconnected with the terminals of a multi-phase alternating voltage sourceas to produce a constantly changing electric field that has a wave-likevariation along the axis about which the electrodes are curved, whichfield tends to repel charged particles in a manner that confines them toa zone near the axis of the electrodes as well as tending to impart tothem a net motion in one direction along that axis.

With these observations and objectives in mind, the manner in which theinvention achieves its purpose will be appreciated from the followingdescription and the accompanying drawings, which exemplifying theinvention, it being understood that changes may be made in the specificapparatus disclosed herein without departing from the essentials of theinvention set forth in the appended claims.

The accompanying drawings illustrate several complete examples ofembodiments of the invention constructed according to the best modes sofar devised for the practical application of the principles thereof, andin which:

FIG. 1 is a more or less diagrammatic view, partly in longitudinalsection and partly in side elevation, illustrating apparatus whichembodies the present invention and which enables particulate material tobe controlledly propelled along a defined generally horizontal path in asubstantially steady stream;

FIG. 2 is another somewhat diagrammatic view, partly in side elevationand partly in section, illustrating a modified form of the general typeof apparatus illustrated in FIG. I, particularly intended for use inelectrostatic powder coating and decorating applications: and

P10. 3 is a generally diagrammatic illustration of another embodiment ofthe invention comprising appara tus by which a gravity produced flow ofparticulate material downwardly from a source thereof to a delivery zonecan be controlled.

Referring now more particularly to the accompanying drawings, thenumeral 26 designates generally a cylindrical tube of dielectricmaterial that defines an elongated generally horizontal'path along whichpowder-like particulate material can be caused to flow in asubstantially steady stream. The tube has a partial closure 27 at itsrear end that leaves an opening 50 through which the lower end portionof a supply duct 48 projects obliquely downwardly and forwardly fordelivery of particulate material into the rear end portion of the tube.It will be understood that the supply duct communicates at its upper endwith a source (not shown) of particulate material and that it conductssuch material into the tube 26 by gravity.

Three insulated elongated electrodes 62, 63, 64 are curved along theirlengths to the form of concentric spirals that surround the tube 26 andclosely embrace its outer periphery. Each of the spiral electrodesextends along the full length of the tube and has a uniform axial pitchalong its length. The three electrodes are spaced apart by small butuniform axial and circumferential distances, as more fully describedbelow.

The three electrodes 62, 63, 64 are respectively connected with theterminals U, V, W of a three-phase ac. voltage source. Attention isdirected to the fact that each electrode is connected with only one ofthe voltage source terminals, and that the connections to the severalelectrodes are such that the alternating voltage applied to each of themis 120 out of phase with that applied to its adjacent electrodes.

As a result of this connection of the electrodes to an a.c. voltagesource, a constantly varying nonuniform electric field is generated bythe several electrodes. Such a field is nonuniform and varying in thesense that its intensity varies from point to point within it at anygiven instant, and, at any given point within it, varies from oneinstant to another during the voltage cycle. As a result, a smallelectrically charged particle in that field is subjected to repulsiveforces that set it into oscillatory motion along curved paths. As morefully explained in the applicants above mentioned copending applicationSer. No. 366,655 (continuation of Ser. No. 151,789), with properconnections of the electrodes to a multi-phase alternating voltagesource, the intensity of the field thus produced changes in a wave-likefashion, so that the oscillations of a charged particle in that fieldwill tend to be unequal, that is, the particle will always tend to movefarther in one direction of its oscillation than in the other, and willthus tend to have a net motion in one direction or another transverselyto the several electrodes producing the field.

The values required for satisfactory operation with charged powderparticles having diameters on the order of one to 100 microns areapproximately as follows:

The electrodes should be of fairly uniform diameter; their diametershould be not more than about 5 cm., and for particles of less than 30microns the electrode diameters should be less than 1 cm.; and thespacing between adjacent electrodes should be about equal to thediameter of an electrode.

Preferably the peak voltage of the applied alternatin voltage should behigh, but should be just low enough to insure that no sparking or arcingtakes place between electrodes. Coating the electrodes with a suitableinsulation (e.g., teflon or epoxy resin) is desirable because it tendsto raise the applied voltage at which arc-over occurs.

The frequency of the alternating voltage should be on the order of to120 Hz. For particles of less than 30 micron diameter the frequency ispreferably below 120 Hz;'for particles of less than 10 micron diameterthe frequency is preferably'below 60 Hz; for particles of less thanthree microns the frequency is preferably below 30 Hz.

It will now be apparent that powdered material that is delivered intothe rear of the tube 26 from the duct 48 tends to fall down onto theinner bottom surface of the tube. But owing to the constantly changingelectric field which exists there, the particles pick up an electriccharge and are repulsively acted upon by the electric field in themanner explained above. Such repulsion confines the particles to a zonenear the axis of the' tube, owing to the fact that the particles areurged away from the spiral electrodes that surround the tube; andbecause the repulsively produced oscillations of the particles areunequal, as explained above, the particles also have a net motion alongthe axis of the tube. If the connections of the several electrodes tothe several terminals of the alternating voltage source are in thecorrect sequence, the direction of such net motion of the particles willbe forwardly, and the particulate material will move to the front end ofthe tube in a stream and at a controlled rate of flow that depends uponthe parameters of the electrodes and the a.c. applied to them. While somoving, the stream of particulate material will be more or lesslevitated in being confined to' a zone near the tube axis and repelledaway from contact with the inner surface of thetube.

FIG. 2 illustrates apparatus generally like that shown in FIG. 1, but ina form which particularly adapts it to applying to a solid article 101 acoating of particulate material obtained from a source 120 thereof. Theapparatus illustrated in FIG. 2 is thus in the nature of an electricfield pump that can be utilized for electrostatic painting, coating,dyeing, pile-planting and similar processes. In this case a tube 26' ofelectrical insulating material that defines a path along which theparticulate material is to be controlledly transported can be a flexibleone, and the elongated electrodes 62, 63, 64 that spiral all along theexterior surface of the tube are secured to it by a flexibleinsulatingcover or coating that not only insulates them from one anotherbut substantially fixes them in relation to the tube and one anotherwhile constraining them to flex with the tube. The dimensions andspacing ofthe electrodes are as described above.

Again, the electrodes are connectable with the terminals U, V, W of athree-phase alternating voltage source, but in this case a switch 40that provides for such connection is so arranged that it can be thrownto an alternative closed position at which the'sequence of connectionsof the electrodes to the terminals is the reverse of that in theillustrated switch-closed position. By reason of such alternative closedpositions of the switch 40, the direction of wave-like variation of theelectric field with time can be reversed, which is to say that,depending upon the position of the switch, particles can be caused tomove either forwardly or rearwardly through the tube 26'.

At its rear end the tube has an upwardly curved end portion or elbow138, and on this elbow portion are arranged electrodes 141, 142, 143that extend generally parallel to the tube axis and are spaced from oneanother at intervals circumferentially around the tube. These axiallyextending electrodes are connected, in a regular sequence around thetube, with the terminals U, V, W of the alternating voltage source, andthey serve to produce a field that repels charged particles from thewall of the elbow portion of the tube, tending to confine them to a zonenear the longitudinal center line of the elbow as they move through itby gravity.

In this case it is not desired to have the particles contact the tubewall to pick up the electrical charge that they need for repulsion bythe electric fields in the tube, and therefore a charge must beimpressed upon them before they enter the tube. Apparatus for impartingsuch a charge to the particles (e.g., known corona discharge apparatus)is designated by 120. Upon leaving the charging apparatus, the particles121 are introduced into an electric field hopper 78 of the typeillustrated in FIG. 3 and described hereinafter, from which they arecontrolledly permitted to fall into the open upper end of the elbow 138.

As shown, the a.c. voltage source comprises step-up transformer means 29that has the neutral side of its secondary connected with a.d.c. voltagesource 102. The voltage of the dc. voltage source is preferablyadjustably variable, as denoted by the oblique arrow through the symbolfor it. Since the dc. voltage source is grounded to the workpiece 101that is to be coated with particulate material, as well as beingconnected to the spiral electrodes 62, 63, 64 as just described, thereis a dc. potential difference between the workpiece 101 and theelectrodes, hence also a potential difference between the workpiece andthe particles; and by reason of this potential difference the particlestend to be attracted to the workpiece, across the space between it andthe front end of the tube.

The hopper illustrated in FIG. 3 provides for control of the gravityflow of particulate material from a source or inlet located above thehopper to a point orzone of use below it. In this case charged particles121 are introduced into the top of the hopper from an outlet at thebottom of an upright inlet duct 77. Near the level of the lower end ofthe duct 77 and concentric with it is a disc 54 of dielectric materialorelectric insulating material that supports a plurality of elongatedelectrodes 56, 57, 56' 57' 56". These electrodes are bent along theirlengths to an annular shape, and they are secured to the underside ofthe insulating disc 54, by means of screws 55, in concentric electrodesso differ in diameter from one another that each is radially spaced fromits neighbors by a distance substantially equal to its diameter. Theseseveral electrodes are so connected with two of the terminals U and W ofa three phase alternating current source that each is connected withonly one of said terminals, which terminal is other than the onethatboth of its radially adjacent electrodes are connected to. Hencethere is a single-phase alternating voltage field beneath the disc 54.

As brought out in more detail in the above mentioned copendingapplication Ser. No. 366,655, the effect of a single-phase alternatingfield'upon charged particles is to set them into an oscillation alongcurved paths, which oscillation carries them substantially equaldistances in both directions of their oscillatory motion so that theyhave no net motion as a result of the electric field itself. However,the single-phase alternating electric field does serve to repel theparticles from the electrodes, forcing them downwardly out of the inletduct 77 and into the body portion of the hopper, and preventingthemfrom-settling on the disc 54 and the several electrodes that it carries.

- Thehopper itself is defined by annular electrodes 59, 60, 59' 60" and65, 66, 67 74. These are generally similar to the above describedannular electrodes that are secured to the disc 54, and, like them, theyare concentric to the upright axis of the hopper. But the electrodes58-60 and 65-74 are vertically spaced from one another, although, again,the vertical distance between each electrode and those adjacent to it isequal to its diameter. The several vertically spaced electrodes can besupported by means of a pair of diametrically opposite upright pillarsor standards 63 of insulating material that also serve to support thedisc 54. Conducting arms 61, secured in an obvious manner by screwthreaded elements 62, extend through the standards 63 and provide forconnection of the vertically spaced apart electrodes with the a.c.voltage source terminals.

Note that the electrodes 59-60" that define the upper portion of thehopper are of substantially equal diameters; whereas each of theelectrodes 65-71 in the medical portion of the hopper has a slightlysmaller diameter than the one above it; while the electrodes 71-74 thatdefine the lowermost part of the hopper are again of uniform diameterand smaller in diameter than those above them. Thus the hopper as awhole that is defined by the several vertically space apart electrodesis more or less funnel-shaped.

The electrodes 59-60" that define the large diameter upper portion ofthe hopper are connected with the terminals U and W of the three-phasevoltage source, each with only one terminal, which terminal is differentfrom the one that its adjacent electrodes are connected to. Henceelectrodes 59-60" repel the charged particles toward the hopper axis andtend to levitate them in the upper portion of the hopper, where theyform a clouldlike accumulation 79.

Since the individual particles of this accumulation 79 have likecharges, they repel one another. Furthermore, the constantly changingintensity of the electric field at any point in the interior of thehopper tends to maintain the particles in a state of agitation whilerepelling them radially. Hence the particulate material of theaccumulation 79 will neither compact into a cohesive mass nor settle onthe solid surfaces of the hopper.

Of course gravity also acts upon the particles, and under its influencethey tend to move downwardly in the hopper.

The electrodes 69-74 that define the lower outlet portion of the hopperare so connectable with all three terminals U, V, W of the voltagesource as to provide a constantly varying potential difference betweenevery pair of adjacent ones of those electrodes, and, as explainedabove, this variation in potential difference produces a wave-likemoving field that tends to repel the particles either upwardly ordownwardly, depending upon the sequence of connection of the severalterminals with the terminals U, V, W as established by the two-positionswitch 40.

It will now be apparent that with the switch 40 in one of its closedpositions, the moving field produced by the electrodes 69-74 propelsparticles downwardly out of the hopper, in effect drawing them down outof the cloud-like accumulation and causing them to be discharged in acontrolled stream, at a rate dependent upon the parameters of theelectrodes and the charging voltage source. A workpiece 101 locatedbeneath the outlet of the hopper can thus be smoothly and evenly coatedwith the particulate material by moving it steadily in a directiontransverse to the hopper axis, as indicated by the arrow to the left ofthe workpiece. Prefe rably the workpiece and the lowermost electrode 74are respectively connected with the opposite terminals of a.d.c. voltagesource that is also connected with the a.c. terminal U to which saidelectrode is connected, to provide for electrostatic attraction ofparticles to the workpiece.

To terminate discharge of particles from the bottom of the hopper, theswitch 40 is thrown to its other closed position. The constantlychanging field now produced by the electrodes 69-74 has a repulsiveeffect upon the particles that tends to impart to them a net upwardmotion, which is to say that said electric field overcomes the force ofgravity upon the particles and confines them to the interior of thehopper, where they remain in a cloud-like accumulation as describedabove. The switch 40 thus provides for control of the flow ofparticulate material with a sort of valving action, although, ascontrasted with a conventional valve, the particles are maintainedout'of contact with solid surfaces while they remain in the hopper and,by being kept in a state of agitation and mutual repulsion, they aresubstantially prevented from cohering to one another so that compactionof the material is prevented and controlled discharge can be resumed assoon as the switch 40 is thrown over to its material dischargingposition.

Since the principles of this invention can be applied to controllingtheflow of particulate material either in supplementing or overcoming theforce of gravity upon the particles, it will be obvious from aconsideration of the last described embodiment of the invention that itis also possible to use apparatus according to the invention for eithersupplementing or overcoming the viscous force which a flowing gasimposes upon particulate material carried in it.

Those skilled in the art will appreciate that the invention can beembodied in forms other than as herein disclosed for purposes ofillustration.

The invention is defined by the following claims:

I claim:

1. Apparatus for controlling the movement of powder-like particulatematerial along an elongated path which is defined by surface areas ofsolid material that surround a longitudinal centerline of said path, andfor confining the particulate material to a zone near said centerlineand against substantial lateral dispersal therefrom into contact withsaid surface areas, said apparatus comprising:

A. a plurality of elongated electrodes, each curved along its length tobe substantially concentric to said centerline, said electrodes beingspaced from one another along said path by substantially uniformdistances, and adjacent electrodes along said path being curved to radiiabout said centerline that differ no more than slightly; and

B. means for connecting each ofthe electrodes with only one of theseveral terminals of a polyphase alternating high voltage source, andwith each of said electrodes connected to a different one of saidterminals than the electrodes that are longitudinally adjacent to italong said path, so that a constantly varying electric field is producedby each pair of the electrodes that are so adjacent whereby particlesare urged toward said centerline, and so that the several electrodescooperate to produce a net electric field of wave-like character thaturges the particles in one direction along said path.

2. The apparatus of claim 1 wherein each of the electrodes issubstantially annular.

3. The apparatus of claim 2 wherein the number of said annularelectrodes is larger than the number of different terminals at saidalternating voltage source, and wherein said means for connectingelectrodes with said terminals provides for connection of a plurality ofelectrodes with each of at least certain of said terminals.

4. The apparatus of claim 1 wherein each of said electrodes is in theform of a spiral extending a substantial distance along said path, andwherein the number voltage source.

ferent terminals at the alternating UNITED STATES PATENT OFFICECERTIFICATE 0F CUECTUFN PATENT NO. 3,872,361

DATED March 18 1975 INVENTOR(S) I SENICHI MASUDA It is certified thaterror appears in the above-identified patent and that said LettersPatent vare hereby corrected as shown below:

Column 2, line 1 "exemplifying should read -exemplify-- Column t line63: "a.d.c." should read --a d.c.-

Column 5 line 21: The following should be inserted after "concentric"-coplanar relation to one another. Note that these-- line r9: "58-60"should read --5960"-- line 52: "about" should be inserted before-equalline 6 L: "medical" should read --medial-- Column 6 line 11:"clould" should read --cloud line H9; "a.d.cfi" should read -"a d.c.

Signed and sealed this 15th day of July 1975,

(SEAL) Attest:

C. MARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officerand Trademarks UNITED STATES PATENT GFFICE CERTIFICATE @E CCRRECTIQNPATENT NO. 3 ,872 ,361

DATED March 18 1975 INVENTOR(S) SENICHI MASUDA It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 2, line in: "exemplifying" should read -exemplify Column t, line63: "a.d .c." should read --a d.c.--

Column 5, line 21: The following should be inserted after "concentriccoplanar relation to one another Note that these-- line t9: 58--60"should read -=--5960"-- line 52: "about" should be inserted before-equalline 6H: "medical" should read medial-- Column 6, line 11:"clould-" should read --cloud line t9: "a.d.c. should read.--a d,c.-

Signed and sealed this 15th day of July 1975 (SEAL) Attest:

C. MARSHALL DANN RUTH C. MASQN Commissioner of Patents Attesting Officerand Trademarks

1. Apparatus for controlling the movement of powder-like particulatematerial along an elongated path which is defined by surface areas ofsolid material that surround a longitudinal centerline of said path, andfor confining the particulate material to a zone near said centerlineand against substantial lateral dispersal therefrom into contact withsaid surface areas, said apparatus comprising: A. a plurality ofelongated electrodes, each curved along its length to be substantiallyconcentric to said centerline, said electrodes being spaced from oneanother along said path by substantially uniform distances, and adjacentelectrodes along said path being curved to radii about said centerlinethat differ no moRe than slightly; and B. means for connecting each ofthe electrodes with only one of the several terminals of a polyphasealternating high voltage source, and with each of said electrodesconnected to a different one of said terminals than the electrodes thatare longitudinally adjacent to it along said path, so that a constantlyvarying electric field is produced by each pair of the electrodes thatare so adjacent whereby particles are urged toward said centerline, andso that the several electrodes cooperate to produce a net electric fieldof wave-like character that urges the particles in one direction alongsaid path.
 2. The apparatus of claim 1 wherein each of the electrodes issubstantially annular.
 3. The apparatus of claim 2 wherein the number ofsaid annular electrodes is larger than the number of different terminalsat said alternating voltage source, and wherein said means forconnecting electrodes with said terminals provides for connection of aplurality of electrodes with each of at least certain of said terminals.4. The apparatus of claim 1 wherein each of said electrodes is in theform of a spiral extending a substantial distance along said path, andwherein the number of such spiral electrodes is equal to the number ofdifferent terminals at the alternating voltage source.